Various devices having been known and used in the machining art for holding and positioning metal workpieces at or on a machine tool for the performance of metal cutting operations to shape the workpiece. Such devices have employed hand operated, pneumatically operated and hydraulically operated clamps to hold the workpiece on the table of the machine tool or on a support or carrier in a position for machining. In some cases the workpiece has been clamped directly to the table of the machine tool while in other cases the workpiece has been clamped to a support or carrier that is in turn fixed to the table of the machine tool. These systems are usually associated with manually operated machine tools and thus the initial individual positioning of the workpiece at or on the machine tool in relation to the cutting tool did not require high accuracy and repeatability since the manual movement of the table and cutting tool could accurately position the workpiece relative to the cutting tool for the correct machining of the part. Thus, there was no need or requirement for the accurate repeatable location of the workpiece relative to the cutting tool.
With the advent of automatic, more especially unmanned automatic, machining operations, by machine tools under numerical control or computer numerical control, on a series of the same or different workpieces serially presented to the cutting tool the workpieces are usually carried on pallets that are moved from a position remote from the cutting tool to a position in an accurate, known location in respect to the cutting tool for the performance of the machining operation. The failure to achieve the repetitive, accurate positioning of the workpieces and the supports or carriers for successive workpieces can result in improper and incorrect machining of the workpiece and thus result in scrap or result in a machine wreck (i.e. high force incorrect engagement of tool with the workpiece) that may damage the machine tool and/or destroy the workpiece. In automated machining systems workpiece carriers or supports having accurately located threaded holes at the intersections of a square grid pattern on one or more faces of the support or carrier and having a T (tee) post, square column, horizontal plate or vertical plate geometry have been used for positioning and holding the workpiece. The square grid pattern of accurately located threaded holes is expensive to produce and allows for the mounting of the workpiece in numerous orientations and locations on the face of the workpiece support or carrier. In automated machining systems such as for example flexible manufacturing systems, requiring numerous workpiece carriers or supports for the efficient operation of the system the expensive nature of the above described square grid pattern type carrier or support is highly magnified. Additionally the square grid pattern of threaded holes in the above described workpiece carrier or support introduces the opportunity for error in the positioning and clamping of the workpiece on the carrier support.
It is an object of this invention to provide an inexpensive workpiece holding fixture apparatus that reproducibly accurately locates, orients and holds a workpiece during machining. Another object of this invention is to provide a workpiece holding fixture apparatus having a detachable workpiece specific mounting plate member to repeatedly accurately locate, orient and hold the workpiece for machining. A still further object of this invention is to provide a workpiece holding fixture apparatus comprising a carrier member, having a surface for detachably mounting a workpiece specific mounting plate member and at the perimeter of the surface locating stop means for accurately locating, the mounting plate on the carrier and cooperating with the accurately located plate a workpiece specific pattern of threaded holes on the workpiece specific mounting plate to reproducibly accurately locate a workpiece for machining.